1 - So easy my 2 year old son could do it by himself.
2 - Requires some skill but nothing out of the range of a typical human being.
3 - Moderately difficult; a good amount of skill and/or determination would be helpful.
4 - Things are getting tricky. This is the project you get half-way into and want to quit, but persevere in finishing only because you're stubborn.
5 - Very difficult. You realize you're out of your league by step 2 in the instructions and lean heavily on help from SuperGoogle, your husband, your dad and your naturally crafty friend/sister/mom to complete. Or you just don't finish it.